1. Field of the Invention
The present invention relates to an IC card and, more particularly, to an IC card which is produced by packaging a semiconductor chip mounted on a film substrate.
2. Description of the Prior Art
Such IC cards have already been put into practical use as having an IC chip such as a semiconductor memory chip (referred to simply as memory chip, hereinunder) or a microcomputer chip packaged on card-type substrates and having memory or computing function.
Briefly, such a known IC card has a comparatively thick wiring substrate and an IC chip mounted on the substrate, the substrate and the IC chip being integrated together with contact terminals so as to form a module-type construction.
FIG. 6 is a sectional view of an essential portion of an IC card produced by a known method. The IC card has a microcomputer chip 1, a memory chip 1', connecting bonding pads 2, 2', bonding wires 3, bonding lead 4, second wiring layer 4', through-holes 5, 5', external contact terminals 6, a wiring substrate 7, resin 8, an IC card center core sheet 9, and an IC card overlay 10.
As will be seen from this Figure, the microcomputer chip 1 and the memory chip 1' are fixed in recesses formed in the multi-layer wiring substrate 7. The bonding pads 2, 2' are connected to the bonding lead 4 through the bonding wires 3. The wiring substrate has three layers: namely, a first wiring layer which constitutes the bonding lead 4, the second wiring layer 4' mentioned above and a third wiring layer which provides externally contact terminals 6. The first wiring layer and the second wiring layer are connected to each other by the through holes 5, while the through holes 5' provide connection between the second wiring layer 4' and the third wiring layer which provides the externally contact terminals 6. The externally contact electrodes 6 are adapted to contact with external terminals on an IC card reader or writer so as to enable the IC card to conduct signal exchange with the IC card reader or writer and to be supplied with electric power.
The wiring substrate 7 having the microcomputer chip 1 and the memory chip 1' are sealed with a resin such as an epoxy resin such that the resin fills the recesses receiving the IC chips and that the resin covers these IC chips, thus presenting a module construction. This module is mounted in a window formed in the center core sheet 9 of the IC card, and the overlay 10 is formed to cover the center core, sheet 9, thus completing the IC card. The externally contact terminals 6, 6 are not covered by the overlay 10 but are exposed for external contact.
In this known IC card, since there are two IC chips, i.e., the microcomputer chip and the memory chip, the wiring construction of the wiring substrate is complicated to require a multi-layer structure. Each IC chip and the wiring substrate are interconnected by a ball bonding method with Au wire, so that the bonding height could not be lower, with the result that the thickness of the module and, hence, the thickness of the IC card are increased.